Interaction of Nitrogen/Phosphorus and Silica/Phosphorus Ratios in Determining Phytoplankton Species Composition and Abundance in Lake George, New York

ABSTRACT

Lake George, New York, is generally considered an oligotrophic phosphorus-limited lake. Yet, the supply and recycling rates of nitrogen and silica may also be critical in regulating phytoplankton productivity, species composition, and abundance. Biweekly phytoplankton bioassays were conducted in 1986 and 1987 at three stations in Lake George to measure the response of natural assemblages to enrichment gradients of nitrogen/phosphorus (N/P) and silica/phosphorus (Si/P). Chlorophyll a concentration, cell number, and species composition were measured throughout the seven to nine day experiments. Limitation by phosphorus, nitrogen, and dissolved silica were observed in the bioassays. Response surface analyses of the bioassay results indicate important interaction of these ratios in determining species composition and seasonal trends in nutrient limitation.